In the prior art, in a drainage vertical tube joint in a drainage ventilation piping structure of single tube type, in order to form swivel flow actively in a waste water flowing in, a reduction guide is installed at lower side of an upper vertical tube connection port, and one or plural swivel guides of spiral shape or blade shape are projected on an inner wall of a taper tube part extending from a swelling part to a lower vertical tube connection port.
Waste water flow subjected to speed reduction and course variation by the reduction guide flows down while supplied with swivel property by the swivel guide, and a ventilation core is formed at the center of the waste water flow flowing down and communication of air of a drainage piping system is intended and pressure variation within the drainage vertical tube is suppressed.
In such a drainage vertical tube joint of conventional construction, however, inner structure of the tube joint becomes quite complicated and there is a problem that clogging is produced due to foreign substance or the like. Also there is a problem that much labor is required for manufacturing the drainage vertical tube joint and the manufacturing cost runs up.